In the Long Term Evolution (LTE) system, an uplink channel sounding reference signal (SRS) is a signal sent to the base station by the user equipment (UE) side, i.e. the terminal and is mainly used by the base station to sound the quality of an uplink channel. According to the result of the sounding, the base station achieves the scheduling of the uplink data, e.g. the frequency resource occupied in uplink transmission, or the modulation coding mode used.
In existing LTE systems, multiple SRS bandwidths are supported. An SRS bandwidth configuration is based on a tree structure and every SRS bandwidth configuration corresponds to one tree structure, wherein, the SRS-Bandwidth of the highest level in the tree structure corresponds to the maximum bandwidth of the SRS bandwidth configuration. The total number of resource blocks (RBs) corresponding to the uplink bandwidth configuration is NRBUL. Tables 1-4 illustrate the SRS bandwidth configurations under different uplink bandwidth configurations. Table 1 corresponds to 6≦NRBUL≦40, Table 2 corresponds to 40<NRBUL≦60, Table 3 corresponds to 60<NRBUL≦80, and Table 4 corresponds to 80<NRBUL≦110.
In these tables, mSRS,b represents the number of RBs contained in every node on the bth level of the tree structure in the frequency domain; when b>0, Nb represents the number of branch nodes of a node on the (b−1)th level, which are located on the bth level of the tree structure; while b=0 corresponds to the highest level of the tree structure, where there must be Nb=1, and mSRS,0 is the maximum SRS bandwidth under the configuration.
TABLE 1SRS-SRS-SRS-SRS-SRS-BandwidthBandwidthBandwidthBandwidthBandwidthb = 0b = 1b = 2b = 3configurationmSRS,0N0mSRS,1N1mSRS,2N2mSRS,3N303611234341132116282422241464141320145414141614441415121434141681424141741414141
TABLE 2SRS-SRS-SRS-SRS-SRS-BandwidthBandwidthBandwidthBandwidthBandwidthb = 0b = 1b = 2b = 3configurationmSRS,0N0mSRS,1N1mSRS,2N2mSRS,3N304812421224314811638242240120245413361123434143211628242524146414162014541417161444141
TABLE 3SRS-SRS-SRS-SRS-SRS-BandwidthBandwidthBandwidthBandwidthBandwidthb = 0b = 1b = 2b = 3configurationmSRS,0N0mSRS,1N1mSRS,2N2mSRS,3N30721243122431641322162442601203454134812421224344811638242540120245416361123434173211628242
TABLE 4SRS-SRS-SRS-SRS-SRS-BandwidthBandwidthBandwidthBandwidthBandwidthb = 0b = 1b = 2b = 3configurationmSRS,0N0mSRS,1N1mSRS,2N2mSRS,3N30961482242461961323162442801402202453721243122434641322162445601203454164812421224374811638242
The frequency domain starting position of the SRS is determined by high layer configured cell-specific SRS bandwidth configuration, UE-specific SRS bandwidth BSRS and frequency domain position parameter nRRC, RRC refers to Radio Resource Control, wherein:
Cell-specific SRS bandwidth configuration parameter: the UE determines the tree structure of the SRS bandwidth, mSRS,b and Nb on every branch corresponding to the tree structure according to the uplink bandwidth and this parameter. This parameter is broadcast in the cell.
UE-specific SRS bandwidth parameter BSRS: it corresponds to one of the four values of b in the above-mentioned tables and is used for determining on which level of the tree structure the SRS is located.
UE-specific SRS frequency domain position parameter nRRC.
According to the tree structure of the SRS bandwidth and the three parameters above mentioned, the SRS frequency domain starting position is determined using the following formula.
                              k          0                =                              k            0            ′                    +                                    ∑                              b                =                0                                            B                SRS                                      ⁢                                                  ⁢                          2              ⁢                                                          ⁢                              M                                  sc                  ,                  b                                RS                            ⁢                              n                b                                                                        (        1        )            
Wherein:
k0 represents the frequency domain starting position of the uplink channel SRS, namely the subcarrier index number.
k′0=(└NNBUL/2┘−mSRS,0/2)NSCRB+kTC, wherein (└NRBUL/2┘−mSRS,0/2)NSCRB ensures that the bandwidth allowed to send the SRS in the system is at the central position of the system bandwidth, └*┘ represents rounding down. NSCRB represents the number of subcarriers contained in an RB in the frequency domain. SC is the abbreviation for “subcarrier”, namely the subcarrier.
kTCε{0,1} is the offset of SRS “Transmission Comb”. The SRS is sent in every other subcarrier in the frequency domain, so it is like a comb in the frequency domain.
Msc,bRS=mSRS,bNscRB/2 represents the length of the SRS sequence at the branch of the bth level in the tree structure.
nb represents the index of a branch node of a node on the (b−1)th level, which is located on the bth level, hence there is nbε{0, 1, 2, . . . , Nb−1}.
nb is calculated according to the frequency domain position parameter nRRC, and the specific correlation between nb and nRRC is related to the way the nRRC is determined.
Currently, there is no specific solutions as to how to determine nRRC, and the frequency domain starting position obtained from the existing solutions is incorrect. Therefore, the SRS frequency domain starting position can not be determined correctly, which leads to the problem that the UE can not send an SRS to the base station at the correct frequency domain starting position, and thus it is difficult for the base station to perform the uplink channel sounding accurately.